JP4639641B2 - Sealed alkaline storage battery - Google Patents

Description

  The present invention relates to a sealed alkaline storage battery.

  The nickel-hydrogen secondary battery uses the same nickel oxide as the nickel-cadmium secondary battery for the positive electrode, and a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen instead of cadmium for the negative electrode. It is the alkaline storage battery used.

  Nickel-hydrogen secondary batteries have energy density approximately 1.5 to 2 times that of nickel-cadmium secondary batteries, flat operating voltage, long charge / discharge cycle life, wide operating temperature range, and safety In recent years, it has been used as a secondary battery for hybrid electric vehicles.

  FIG. 8 is a diagram for explaining charging of the nickel-hydrogen secondary battery.

Referring to FIG. 8, nickel-hydrogen secondary battery 100 includes a positive electrode 104, a negative electrode 106, and a separator 108 that separates the positive electrode and the negative electrode in an alkaline electrolyte. The positive electrode 104 is nickel oxide, and the negative electrode 106 is a hydrogen storage alloy. When charging is performed by connecting the charger 102 to the nickel-hydrogen secondary battery 100, a charging reaction represented by the following formula (1) occurs at the positive electrode.
Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1)
In the negative electrode, a charging reaction represented by the following formula (2) occurs.
M + H ₂ O + e ⁻ → MH + OH ⁻ (2)
Since water and OH ^- ions permeate through the separator 108, the charging reaction of the entire battery is expressed by the following equation (3).
M + Ni (OH) ₂ → MH + NiOOH (3)
Although the charging operation has been described with reference to FIG. 8, a discharging reaction opposite to the charging reaction occurs during discharging.

  By the way, the nickel-hydrogen secondary battery has a protection function against overcharge and overdischarge in principle, and is very easy to seal.

  Specifically, as in the case of the nickel-cadmium secondary battery, the nickel-hydrogen secondary battery adopts a so-called positive electrode regulation method using a negative electrode having a capacity that is about 50% larger than that of the positive electrode. Gas generation occurs only at the positive electrode during overcharge or overdischarge, and the generated gas is consumed on the negative electrode.

  FIG. 9 is a diagram for explaining a positive electrode regulating method of a nickel-hydrogen secondary battery.

  Referring to FIG. 9, the lengths of the positive and negative electrode bars indicate the capacity of each electrode. The fact that the negative electrode is longer than the positive electrode corresponds to the capacity of the negative electrode being about 50% larger than that of the positive electrode. The hatched portion corresponds to the hatched portion in FIG. 8, and the hatched portion of the positive electrode indicates the ratio of the positive electrode being NiOOH due to the charging action. Moreover, the hatching part in a negative electrode shows the ratio by which the negative electrode is set to MH by charging action.

  When charging is advanced from the intermediate state shown in FIG. 9B, the positive electrode is in a state where the charging reaction does not proceed any more as shown in FIG. 9A, but the negative electrode is extraneous so that hydrogen is not generated during overcharging. An uncharged portion (charging reserve) that can be charged is provided.

  Next, when the discharge of the battery proceeds from the intermediate state of FIG. 9B, as shown in FIG. 9C, the positive electrode is in a state where no more normal discharge reaction occurs, but the negative electrode has oxygen during overdischarge. A charging portion (discharge reserve) that can be discharged excessively is provided so as not to occur.

Here, the protection function at the time of overcharge by a positive electrode control system is demonstrated. Consider an overcharge state in which charging has been performed further than in the fully charged state of FIG. In the positive electrode, oxygen is generated by the reaction represented by the following formula (4).
OH ⁻ → 1/4 O ₂ + 1 / 2H ₂ O + e ⁻ (4)
Oxygen generated at the positive electrode permeates the separator and reaches the negative electrode, where it is consumed by reaction with the metal hydride represented by the following formula (5).
MH + 1 / 4O ₂ → M + 1 / 2H ₂ O (5)
Note that the MH content decreased in the equation (5) is compensated by the negative electrode charging reaction represented by the following equation (6).
M + H ₂ O + e ⁻ → MH + OH ⁻ (6)
Eventually, the reaction of the negative electrode during overcharge is expressed by the following equation (7).
1/4 O ₂ + 1 / 2H ₂ O + e ⁻ → OH ⁻ (7)
That is, the reaction of the positive electrode is represented by the above formula (4), the reaction of the negative electrode is represented by the formula (7), and oxygen generated at the positive electrode is consumed at the negative electrode. It will not happen. As a result, there is almost no increase in the battery internal pressure due to oxygen during overcharge.

  Further, during overdischarge, hydrogen is generated at the positive electrode, but this hydrogen passes through the separator and reaches the negative electrode and is consumed at the negative electrode, so that no apparent reaction occurs in the entire battery.

  Thus, the nickel-hydrogen secondary battery is provided with an appropriate charge reserve and discharge reserve on the negative electrode so that gas generated at the time of overcharge or overdischarge is consumed at the negative electrode.

  As described above, the nickel-hydrogen secondary battery is a battery in which an increase in internal pressure due to gas generation is unlikely to occur. is there.

Japanese Patent Application Laid-Open No. 8-212994 (Patent Document 1) discloses an alkaline storage battery having a safety valve made of rubber in order to release gas to the outside of the battery and prevent bursting even when a sudden pressure rise occurs in the battery. Is disclosed. This alkaline storage battery is provided with a second safety valve formed of a ring-shaped elastic valve body around a rubber safety valve for further certainty.
JP-A-8-212994 Japanese Patent Publication No. 7-15812 JP 2000-340254 A JP 2001-15391 A JP 2003-77527 A JP 2004-31167 A

  The battery case of the sealed alkaline storage battery is made of metal or resin.

  Although the resin battery case is easy and light to process, there is a problem that hydrogen gas and the like easily pass through the battery case. In particular, in a nickel-hydrogen secondary battery using a hydrogen storage alloy, if the hydrogen in the battery case decreases as hydrogen passes through the battery case, the discharge reserve amount and the charge reserve amount described in FIG. 9 are set. As a result, the capacity balance between the negative electrode and the negative electrode is lost, and the characteristics are greatly deteriorated.

  That is, it is considered that when hydrogen is released from the inside of the battery case, the hydrogen partial pressure inside the battery case is lowered, so that hydrogen is released from the hydrogen storage alloy and the discharge reserve amount is reduced. When the discharge reserve amount is reduced to zero, the battery characteristics are greatly deteriorated.

  On the other hand, if a metal battery case is used, since there is almost no permeation of hydrogen, there is no problem that the discharge reserve amount of the negative electrode is reduced.

However, secondary batteries for hybrid vehicles are required to have a very long life. While the hydrogen-nickel secondary battery is used for a long time, oxidation of the hydrogen storage alloy of the negative electrode occurs. This oxidation is performed using H ₂ O in the electrolytic solution. Then, hydrogen H ₂ is generated at the negative electrode along with the oxidation. The generated hydrogen is stored in the hydrogen storage alloy of the negative electrode, which causes the balance between the discharge reserve and the charge reserve to be lost.

  FIG. 10 is a schematic diagram showing a state where hydrogen is occluded in the negative electrode and the balance between the discharge reserve and the charge reserve is lost.

  Referring to FIG. 10, in the intermediate state of (b), as compared with the intermediate state of FIG. 9 (b), hydrogen generated by the oxidation reaction of the negative electrode is occluded in the negative electrode, and the charged state of the negative electrode, that is, hydrogen occlusion. The state is increasing.

  Thus, when the balance between the charged state of the positive electrode and the negative electrode is lost, the charge reserve is reduced at the time of full charge of (a) compared to the case of FIG. It becomes the state increased compared to 9.

  In many cases, the state of charge of the secondary battery in a hybrid vehicle is monitored by monitoring the state of charge of the positive electrode with a computer. For this reason, it is determined that the charged state of the positive electrode is insufficient even at the time of full charge in FIG.

  At this time, if the charge reserve at the negative electrode is reduced, if not noticed, overcharge occurs, and hydrogen gas is generated at the negative electrode. When hydrogen gas is generated and the pressure is increased, the safety valve is actuated to reduce the internal electrolyte, resulting in a problem that the battery life is shortened.

  An object of the present invention is to provide a sealed alkaline storage battery having a long battery life.

  In summary, this invention is a sealed alkaline storage battery, and includes a positive electrode, a negative electrode, and a container that accommodates the positive electrode and the negative electrode. The container includes first and second parts using first and second materials having different hydrogen permeability. The permeation amount of hydrogen released from the inside of the container to the outside is adjusted to a predetermined value.

  Preferably, the first part is a metal case, and the second part is a valve body of a safety valve using a hydrogen permeable material.

  More preferably, the valve body is made of rubber having hydrogen permeability.

  More preferably, the valve body has a shape in which at least a part of the thickness is thinner than the other part.

  More preferably, the valve body is provided with irregularities on the surface so as to increase the surface area.

  Preferably, the sealed alkaline storage battery is a nickel-hydrogen secondary battery.

  According to the present invention, an appropriate amount of hydrogen can be released with a simple configuration, and a long-life sealed alkaline storage battery can be realized while utilizing the existing battery pack shape as it is.

  FIG. 1 is a view showing the appearance of a sealed alkaline storage battery 1 of the present invention.

  Referring to FIG. 1, sealed alkaline storage battery 1 includes a metal case 2 that is a battery case, and a safety valve 4 provided on the top of metal case 2.

The metal case 2 contains the positive electrode 104, the negative electrode 106, and the separator 108 as described with reference to FIG. In the case of a nickel-hydrogen secondary battery, general members can be used as the members. For example, the positive electrode 104 can be a positive electrode plate including foamed nickel and a mixture filled in the foamed nickel. The mixture contains an active material mainly composed of nickel hydroxide and cobalt having a valence of less than three. Examples of cobalt having a valence of less than 3 include cobalt metal and cobalt in Co (OH) ₂ .

  As the negative electrode 106, for example, a hydrogen storage alloy containing aluminum, cobalt, and manganese can be used.

  As the separator 108, for example, a sulfonated polypropylene separator can be used. An alkaline aqueous solution containing potassium hydroxide as a main solute can be used as the electrolytic solution.

  2 is a cross-sectional view of the sealed alkaline storage battery container shown in FIG.

  Referring to FIG. 2, a safety valve 4 is provided on the upper part of the metal case 2. The safety valve 4 includes a valve body 8 made of a rubber material having a high hydrogen permeability and a support member 6 for holding the valve body 8. A hole is provided in the upper center of the support member 6, and a hole is also provided in the upper part of the metal case 2. The two holes are pressed against the valve body 8.

  If the pressure in the metal case 2 rises abnormally, the valve body 8 is deformed for safety, and a gap formed between the valve body 8 and the metal case 2 and between the valve body 8 and the support member 6 are generated. Internal gas and moisture are released from the gap.

  Further, since the valve body 8 is made of a rubber material having a high hydrogen permeability, if the internal pressure is such that the valve body 8 is not deformed, the hole portion of the metal case 2 pressed against the valve body 8 is formed. Hydrogen gas generated by the oxidation of the electrode permeates.

  As the material of the valve body 8, for example, EPDM (ethylene-propylene terpolymer) rubber or silicon rubber which is a rubber material having a relatively high hydrogen permeability can be used.

  The metal case is characterized by improved cooling and less hydrogen removal. In the short term, it is preferable that hydrogen does not escape more easily than the resin case. However, if hydrogen does not escape much, hydrogen generated by oxidation of the electrode will not escape due to long-term use. Charging reserve is reduced.

  The present invention is characterized in that hydrogen gas is actively released from the valve body by employing a rubber material having hydrogen permeability for the valve body 8. However, if hydrogen permeation is caused as much as using a resin case, the charge reserve will increase and the discharge reserve will decrease, and the balance will be lost, so the amount of hydrogen gas permeated from the valve body must be set appropriately. is required.

  That is, the amount of hydrogen gas that permeates is determined according to the amount of hydrogen gas generated by oxidation of the negative electrode taking into account the surface area of the negative electrode, the amount of the electrolyte, and the like.

  FIG. 3 is an enlarged view of the vicinity of the safety valve 4 of FIG.

  Referring to FIG. 3, the surface area A of the opening of the metal case 2 that is in contact with the valve body 8 is set to an appropriate value, and the thickness D of the valve body 8 is tuned to an appropriate value. In order to positively increase the hydrogen permeation amount of the valve body portion of the rubber, the surface area A is increased and the rubber thickness D is decreased.

  FIG. 4 is a view showing a first modification of the valve body of the safety valve.

  Referring to FIG. 4, the valve body 8 </ b> A of the safety valve has a shape in which at least a part is thinner than the other part. Specifically, the center of the portion in contact with the opening of the metal case 2 is recessed and thinned. Thereby, the hydrogen permeation amount can be increased.

  FIG. 5 is a view for explaining a second modification of the valve body of the safety valve.

  6 is a view showing a VI-VI cross section in FIG.

  5 and 6, the surface of the valve body 8A shown in FIG. 4 is provided with fine irregularities so as to increase the surface area. Thereby, the valve body 8B further increases the hydrogen permeation amount compared to the valve body 8 and the valve body 8A.

  FIG. 7 is a diagram for explaining a change in the negative electrode discharge reserve of the sealed alkaline storage battery of the present invention.

  Referring to FIG. 7, in the case of the resin case, the discharge reserve amount of the negative electrode decreases year by year because the hydrogen storage alloy releases hydrogen when hydrogen gas permeates the resin case and leaks to the outside due to aging. The discharge reserve amount becomes zero.

  On the other hand, if a metal case is used and a safety valve structure that does not consider hydrogen permeation like a normal safety valve has occurred, the discharge reserve amount of the negative electrode increases due to hydrogen generated by the oxidation reaction of the negative electrode over time, and charging The reserve amount will decrease.

  On the other hand, in the battery of the present invention, the discharge reserve amount of the negative electrode can be kept substantially constant by appropriately adjusting the hydrogen permeation amount. And the change of the internal pressure at the time of overcharge or overdischarge hardly occurs. For this reason, since it becomes difficult to generate | occur | produce that a safety valve act | operates and internal electrolyte solution is lost, the lifetime of a battery can be extended.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is the figure which showed the external appearance of the sealed alkaline storage battery 1 of this invention. It is sectional drawing of the container of the sealed alkaline storage battery shown in FIG. FIG. 3 is an enlarged view of the vicinity of the safety valve 4 in FIG. 2. It is the figure which showed the 1st modification of the valve body of a safety valve. It is a figure for demonstrating the 2nd modification of the valve body of a safety valve. It is the figure which showed the VI-VI cross section in FIG. It is a figure for demonstrating the change of the negative electrode discharge reserve amount of the sealed alkaline storage battery of this invention. It is a figure for demonstrating charge of a nickel-hydrogen secondary battery. It is a figure for demonstrating the positive electrode control system of a nickel-hydrogen secondary battery. It is the schematic diagram which showed the state by which hydrogen was occluded by the negative electrode and the balance of discharge reserve and charge reserve was broken.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Sealed alkaline storage battery, 2 Metal case, 4 Safety valve, 6 Support member, 8,8A, 8B Valve body, 100 Nickel-hydrogen secondary battery, 102 Charger, 104 Positive electrode, 106 Negative electrode, 108 Separator.

Claims (5)

A positive electrode;
A negative electrode,
A container containing the positive electrode and the negative electrode,
The container is
A metal case,
Including a safety valve having a valve body using a hydrogen permeable material,
The valve body is a sealed alkaline storage battery in which the permeation amount of hydrogen released from the inside of the container to the outside is adjusted so that hydrogen gas generated by the oxidation of the electrode can permeate . The sealed alkaline storage battery according to claim 1 , wherein the valve body is made of rubber having hydrogen permeability. 2. The sealed alkaline storage battery according to claim 1 , wherein the valve body has a shape in which at least a part of the thickness is thinner than another part. The sealed alkaline storage battery according to claim 1 , wherein the valve body is provided with irregularities on a surface so as to increase a surface area. The sealed alkaline storage battery according to any one of claims 1 to 4 , wherein the sealed alkaline storage battery is a nickel-hydrogen secondary battery.

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